# Optima RTR-4.2 · Car battery 12V 50Ah 815A

![Optima RTR-4.2 · Car battery 12V 50Ah 815A](https://bateriasonline.es/3858-home_default/optima-rtr-4-2.jpg)

> Optima RTR-4.2 (ETN 803251000): 50 Ah car battery, 815 A (EN), 254×175×200 mm, positive terminal on the right. Equivalent to Optima RTC-4.2.

**Category:** [Car batteries](https://bateriasonline.es/en/car-batteries) → [Optima](https://bateriasonline.es/en/optima-batteries)

- **Canonical URL**: https://bateriasonline.es/en/optima-rtr-4-2
- **Language**: en
- **Brand**: Optima
- **Reference**: BOL-OPTIMA-RTR-4.2
- **EAN**: 4016987113479
- **MPN**: RTR-4.2
- **Price**: 205,42 € (VAT incl., Spain)
- **Last updated**: 2026-10-27

## Technical specifications

| Feature | Value |
|---|---|
| Brand | Optima |
| Range | OPTIMA RED TOP |
| Application | Cars |
| Technology | Spiral AGM |
| Voltage | 12 V |
| Capacity | 50 Ah |
| Cold cranking amps (EN) | 815 A |
| Length | 254 mm |
| Width | 175 mm |
| Height | 200 mm |
| Weight | 18 kg |
| Polarity | Positive terminal on the right |
| ETN code | 803251000 |

## Quick description

The Optima RTR-4.2 (ETN 803 251 000, also written 803251000) is a car battery (spiral AGM) with 12 V, 50 Ah and 815 A cold cranking current, measuring 254 × 175 × 200 mm, with the positive terminal on the right. If yours has the positive terminal on the left, you need the Optima RTS-4.2.

## Description

## Who the Optima RTR-4.2 is for

The Optima RTR-4.2 is a starter battery for cars without Start-Stop: it delivers the current the starter motor needs and then powers lights, control units and audio with the engine off. Its job is to start the engine in the cold with margin to spare and keep the car's electronics powered.
At 50 Ah it covers petrol compacts and small diesels, the best-selling format in Europe. The RTR-4.2 belongs to the Optima OPTIMA RED TOP range. [The full range of Optima batteries](https://bateriasonline.es/en/optima-batteries)

## Optima RTR-4.2 codes and part numbers

The RTR-4.2 is listed under these codes on labels, in garages and in catalogues:

| Commercial reference | RTR-4.2 |
|---|---|
| ETN code | 803251000 (also 803 251 000) |
| EAN | 4016987113479 |
| Case size according to Optima | 34R (BCI) |
| Base hold-down | B11 |
| Also known as | Optima 803251000 · Optima 803 251 000 |
| Not to be confused with | Optima RTC-4.2 (50 Ah, 815 A), Optima RTF-4.2 (50 Ah, 815 A, positive terminal on the left), Optima RTS-4.2 (50 Ah, 815 A, positive terminal on the left) |

## Optima RTR-4.2 vs RTR-3.7 and RTS-4.2: differences

How the RTR-4.2 compares with Optima batteries of similar size and capacity:

| Model | Capacity | Cold cranking (EN) | Dimensions (mm) | Positive | Weight |
|---|---|---|---|---|---|
| Optima RTR-4.2 (this one) | 50 Ah | 815 A | 254 × 175 × 200 | right | 18 kg |
| Optima RTR-3.7 | 44 Ah | 730 A | 237 × 172 × 197 | right | 15.6 kg |
| Optima RTS-4.2 | 50 Ah | 815 A | 254 × 175 × 200 | left | 18 kg |

- Optima RTR-3.7: 6 Ah less, 85 A less cranking power, a different case (237 × 172 × 197 mm).
- If the positive terminal of your battery is on the other side, the one you need is the Optima RTS-4.2 (positive terminal on the left).

## Equivalents and alternatives to the Optima RTR-4.2

As the RTR-4.2 is an AGM battery, we only list other AGM batteries with its dimensions and polarity: neither an EFB nor a conventional battery can replace it.

| Model | Technology | Capacity | Cold cranking (EN) | Dimensions (mm) |
|---|---|---|---|---|
| Optima RTC-4.2 | Spiral AGM | 50 Ah | 815 A | 254 × 175 × 200 |

## Spiral AGM technology in the RTR-4.2

The RTR-4.2 is a spiral-cell AGM battery. Perfect for 4x4s, marine use and vehicles with lots of electronics.

## Check this before ordering the Optima RTR-4.2

- The RTR-4.2 is AGM: it replaces an AGM or an EFB of the same size. You can swap an EFB for an AGM, but not an AGM for an EFB.
- The RTR-4.2 delivers 815 A cold cranking (EN standard); do not go below what your original battery states.
- Your current battery should say about 50 Ah; a little more is also fine.
- The RTR-4.2 has the positive terminal on the right: compare it with your current battery.
- Measure the space: the RTR-4.2 takes up 254 × 175 × 200 mm.

## Frequently asked questions about the Optima RTR-4.2

### Optima RTR-4.2 or RTR-3.7?

Compared with the RTR-4.2, the Optima RTR-3.7 has 6 Ah less and 85 A less cranking power. The RTR-4.2 cranks harder; the RTR-3.7 is only a good option if your original battery says 730 A or less. Mind the space: the RTR-3.7 measures 237 × 172 × 197 mm.

### What is the difference between the Optima RTR-4.2 and the RTS-4.2?

They are the same battery with the terminals swapped: positive terminal on the right on the RTR-4.2, positive terminal on the left on the RTS-4.2. Look at your current battery with the terminals facing you and pick the one that matches. That is why their ETNs only differ in the middle group: 803 251 000 for the RTR-4.2 and 802 250 000 for the RTS-4.2.

### What is the ETN code of the Optima RTR-4.2?

803251000, also written 803 251 000. The ETN (European Type Number) is printed on the label and used in parts catalogues.

### Can the Optima RTR-4.2 be used in a car with Start-Stop?

Yes. As an AGM battery, the RTR-4.2 handles automatic engine stop and brake energy recovery, and it can replace an EFB of the same size.

### How much does the Optima RTR-4.2 weigh?

The RTR-4.2 weighs 18 kg. For reference, the Optima RTR-3.7 (44 Ah) weighs 15.6 kg.

### Which battery is equivalent to the Optima RTR-4.2?

Only other AGM batteries with its dimensions and polarity: Optima RTC-4.2. Neither an EFB nor a conventional battery replaces the RTR-4.2.

### Does the new battery need to be registered in the car?

In cars with energy management (common since 2010) it is worth registering the battery in the control unit so it adjusts charging. In older cars you just connect it.

## Keep comparing: alternatives to the RTR-4.2

- [More car batteries](https://bateriasonline.es/en/car-batteries)
- [The whole Optima range](https://bateriasonline.es/en/optima-batteries)
- [Optima RTC-4.2](https://bateriasonline.es/en/optima-rtc-4-2) · 50 Ah, 815 A, 254×175×200 mm

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*bateriasonline.es — Batteries and accessories · 2026-11-10*